Method for measuring and reporting channel quality in a broadband wireless access communication system

ABSTRACT

A method for measuring/reporting a channel quality in a broadband wireless access communication system. The method for reporting channel qualities of active BS and neighbor BSs measured by an MSS to the active BS when the MSS exists in a specific area covered by the active BS and neighbor BSs in a communication system includes the steps of: a) receiving channel quality report information indicative of channel periods of the channel qualities from the active BS, and receiving channel quality measurement information associated with individual channel qualities of the neighbor BSs and the active BS from the active BS; b) measuring SINRs of the neighbor BSs and the active BS according to the channel quality measurement information; and c) reporting the measured SINRs of the neighbor BSs and the active BS to the active BS.

PRIORITY

[0001] This application claims priority to an application entitled“METHOD FOR MEASURING/REPORTING CHANNEL QUALITY IN BROADBAND WIRELESSACCESS COMMUNICATION SYSTEM”, filed in the Korean Intellectual PropertyOffice on Apr. 30, 2003 and assigned Serial No. 2003-27885, the contentsof which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to a broadband wirelessaccess communication system, and more particularly to a method formeasuring and reporting a channel quality in a broadband wireless accesscommunication system for use with an OFDM (Orthogonal Frequency DivisionMultiplexing) scheme.

[0004] 2. Description of the Related Art

[0005] A great deal of intensive research has been conducted on the 4G(4th Generation) communication system as one of the next generationcommunication systems to provide a plurality of users with a specificservice having a variety of QoSs (Quality of Services) at a transferrate of about 100 Mbps. Presently, the 3G (3rd Generation) communicationsystem provides a transfer rate of about 384 kbps in an outdoor channelenvironment having a relatively poor channel environment, and provides amaximum transfer rate of about 2 Mbps in an indoor channel environmenthaving a relatively good channel environment. A wireless Local AreaNetwork (LAN) system and a wireless Metropolitan Area Network (MAN)system have been designed to provide a transfer rate of 20˜50 Mbps.Further, a new communication system based on the 4G communication systemhas been developed to provide the wireless LAN and MAN systems forguaranteeing a relatively high transfer rate with mobility and QoS. As aresult, many developers have conducted intensive research into ahigh-speed service to be provided from the 4G communication system.

[0006] However, the wireless MAN system is suitable for a high-speedcommunication service in that it has a wide coverage and supports ahigh-speed transfer rate, but it does not consider the mobility of asubscriber station (SS). Consequently, there is no consideration of ahandover operation caused by the high-speed movement of the SS. Thecommunication system currently considered in the IEEE (Institute ofElectrical and Electronics Engineers) 802.16a specification acts as aspecific communication system for performing a ranging operation betweenthe SS and a base station (BS). FIG.

[0007]FIG. 1 is a block diagram illustrating a broadband wireless accesscommunication system using an OFDM/OFDMA (Orthogonal Frequency DivisionMultiplexing/Orthogonal Frequency Division Multiple Access) scheme. Morespecifically, FIG. 1 depicts the IEEE 802.16a communication system.

[0008] The wireless MAN system acting as a BWA (Broadband WirelessAccess) communication system has a much wider coverage and a much highertransfer rate than the wireless LAN system. When adapting the OFDMscheme and the OFDMA scheme to a physical channel of the wireless MANsystem to provide the wireless MAN system with a broadband transmissionnetwork, this application system is called an IEEE 802.16a communicationsystem. The IEEE 802.16a communication system applies the OFDM/OFDMAscheme to the wireless MAN system, such that it transmits a physicalchannel signal using a plurality of sub-carriers, resulting inhigh-speed data transmission.

[0009] The IEEE 802.16e communication system has been designed toconsider the SS's mobility in the IEEE 802.16a communication system, andthere is no detailed specification for the IEEE 802.16e communicationsystem. The IEEE 802.16a communication system and the IEEE 802.16ecommunication system act as a broadband wireless access communicationsystem for use with the OFDM/OFDMA schemes. For the convenience ofdescription, the IEEE 802.16a communication system will be adapted as anexample.

[0010] Referring to FIG. 1, the IEEE 802.16a communication system has asingle cell structure, and comprises a BS 100 and a plurality of SSs110, 120, and 130, which are managed by the BS 100. Signaltransmission/reception among the BS 100 and the SSs 110, 120, and 130can be established using the OFDM/OFDMA scheme. FIG.

[0011]FIG. 2 is a conceptual diagram illustrating the downlink framestructure for use in the BWA communication system using the OFDM/OFDMAscheme. More specifically, FIG. 2 depicts a downlink frame structure foruse in the IEEE 802.16a/IEEE 802.16e communication system.

[0012] Referring to FIG. 2, the downlink frame includes a preamble field200, a broadcast control field 210, and a plurality of TDM (TimeDivision Multiplexing) fields 220 and 230. A synchronous signal (i.e., apreamble sequence) for synchronizing the BS and the SSs is transmittedvia the preamble field 200. The broadcast control field 210 includes aDL(DownLink)_MAP field 211 and a UL(UpLink)_MAP field 213. The DL_MAPfield 211 transmits the DL_MAP message. A plurality of IEs (InformationElements) contained in the DL_MAP message are shown in Table 1 below.TABLE 1 Syntax Size Notes DL_MAP_Message_Format( ){ Management MessageType=2  8 bits PHY Synchronization Field Variable See Appropriate PHYspecification DCD Count  8 bits Base Station ID 48 bits Number of DL_MAPElement n 16 bits Begin PHY Specific section { See Applicable PHYsection  For (i=1; i<=n; i++) For each DL_MAP element 1 to n DL_MAPInformation Element( ) Variable See corresponding PHY specification if!(byte boundary) {  4 bits Padding to reach byte    Padding Nibbleboundary          }        }      }    }

[0013] Referring to Table 1, the DL_MAP message includes a ManagementMessage Type field including a plurality of IEs (i.e., transmissionmessage type information); a PHY (PHYsical) Synchronization fieldestablished in response to a modulation or demodulation scheme appliedto a physical channel in order to perform synchronization acquisition; aDCD count field including count information in response to a DCD(Downlink Channel Descript) message configuration variation containing adownlink burst profile; a Base Station ID field including a Base StationIdentifier; and a Number of DL_MAP Element n field including the numberof elements found after the Base Station ID. Particularly, the DL_MAPmessage (not shown in Table 1) includes information associated withranging codes allocated to individual ranging processes to be describedlater.

[0014] The UL_MAP field 213 transmits the UL_MAP message. A plurality ofIEs contained in the UL_MAP message are shown in Table 2 below. TABLE 2Syntax Size Notes UL_MAP_Message_Format( ){ Management Message Type=3  8bits Uplink Channel ID  8 bits UCD Count  8 bits Number of UL_MAPElement n 16 bits Allocation Start Time 32 bits Begin PHY Specificsection { See Applicable PHY section  for (I=1; i<=n; i++) For eachDL_MAP element 1 to n UL_MAP Information_Element( ) Variable Seecorresponding PHY specification           }         }       }

[0015] Referring to Table 2, the UL_MAP message includes a ManagementMessage Type field including a plurality of IEs (i.e., transmissionmessage type information); an Uplink Channel ID field including a usedUplink Channel ID; a UCD (Uplink Channel Descript) count field includingcount information in response to a UCD message configuration variationcontaining an uplink burst profile; and a Number of UL_MAP Element nfield including the number of elements found after the UCD count field.In this case, the uplink channel ID can only be allocated to a MediaAccess Control (MAC) sub-layer.

[0016] The TDM fields 220 and 230 are timeslots using a TDM/TDMA (TimeDivision Multiple/Time Division Multiple Access) scheme. The BStransmits broadcast information to be broadcast to SSs managed by the BSover the DL_MAP field 211 using a predetermined center carrier. The SSsmonitor all the frequency bands having been previously allocated toindividual SSs upon receipt of a power-on signal, such that they detecta pilot channel signal having a highest signal intensity, i.e., thehighest SINR (Signal to Interference and Noise Ratio). It is determinedthat the SS belongs to a specific BS, which has transmitted the pilotchannel signal with the highest SINR. The SSs check the DL_MAP field 211and the UL_MAP field 213 of the downlink frame transmitted from the BS,such that they recognize their own uplink and downlink controlinformation and specific information for indicating a real datatransmission/reception position.

[0017] The aforementioned UCD message configuration is shown in Table 3below. TABLE 3 Syntax Size Notes UCD-Message_Format( ){ ManagementMessage Type=0 8 bits Unlink channel ID 8 bits Configuration ChangeCount 8 bits Mini-slot size 8 bits Ranging Backoff Start 8 bits RangingBackoff End 8 bits Request Backoff Start 8 bits Request Backoff End 8bits TLV Encoded Information for the Variable overall channel Begin PHYSpecific Section {  for (I=1; i<n; i+n)   Uplink_Burst_DescriptorVariable   }  } }

[0018] Referring to Table 3, the UCD message includes a ManagementMessage Type field including a plurality of IEs (i.e., transmissionmessage type information); an Uplink Channel ID field including a usedUplink Channel Identifier; a Configuration Change Count field counted bythe BS; a mini-slot size field including the size of the mini-slot ofthe uplink physical channel; a Ranging Backoff Start field including abackoff start point for an initial ranging process, i.e., an initialbackoff window size for the initial ranging process; a Ranging BackoffEnd field including a backoff end point for the initial ranging process,i.e., a final backoff window size; a Request Backoff Start fieldincluding a backoff start point for establishing contention data andrequests, i.e., an initial backoff window size; and a Request BackoffEnd field including a backoff end point for establishing contention dataand requests, i.e., a final backoff window size. In this case, thebackoff value indicates a kind of standby time which is a duration timebetween the start of SS's access failure and the start of SS's re-accesstime. If the SS fails to execute an initial ranging process, the BS musttransmit the backoff values indicative of standby time information forwhich the SS must wait for the next ranging process to the SS. Forexample, provided that a specific number of 10 is determined by the“Ranging Backoff Start” and “Ranging Backoff End” fields shown in theTable 3, the SS must pass over 2¹⁰ access executable chances (i.e., 1024access executable chances) and then execute the next ranging processaccording to the Truncated Binary Exponential Backoff Algorithm.

[0019]FIG. 3 is a conceptual diagram illustrating an uplink framestructure for use in a BWA communication system using an OFDM/OFDMAscheme. More specifically, FIG. 3 depicts an uplink frame structure foruse in the IEEE 802.16a communication system.

[0020] Prior to describing the uplink frame structure illustrated inFIG. 3, three ranging processes for use in the IEEE 802.16acommunication system, i.e., an initial ranging process, a maintenanceranging process (also called a period ranging process), and a bandwidthrequest ranging process will hereinafter be described in detail.

[0021] The initial ranging process for establishing synchronizationacquisition between the BS and the SS establishes a correct time offsetbetween the SS and the BS, and controls a transmission power (alsocalled a transmit power). More specifically, the SS is powered on, andreceives the DL_MAP message, the UL_MAP message, and the UCD message toestablish synchronization with the BS in such a way that it performs theinitial ranging process to control the transmission power between the BSand the time offset. In this case, the IEEE 802.16a communication systemuses the OFDM/OFDMA scheme, such that the ranging procedure requires aplurality of ranging sub-channels and a plurality of ranging codes. TheBS allocates available ranging codes to the SS according to objectivesof the ranging processes (i.e., the ranging process type information).This operation will hereinafter be described in more detail.

[0022] The ranging codes are created by segmenting a PN (PseudorandomNoise) sequence having a length of 2¹⁵−1 bits into predetermined units.Typically, one ranging channel is composed of two ranging sub-channelseach having a length of 53 bits, PN code segmentation is executed overthe ranging channel having the length of 106 bits, resulting in thecreation of a ranging code. A maximum of 48 ranging codes RC#1˜RC#48 canbe assigned to the SS. More than two ranging codes for every SS areapplied as a default value to the three ranging processes havingdifferent objectives, i.e., an initial ranging process, a period rangingprocess, and a bandwidth request ranging process. In this way, a rangingcode is differently assigned to the SS according to each objective ofthe three ranging processes. For example, N ranging codes are assignedto the SS for the initial ranging process as denoted by a prescribedterm of “N RC (Ranging Codes) for Initial Ranging”, M ranging codes areassigned to the SS for the periodic ranging process as denoted by aprescribed term of “M RCs for maintenance ranging”, and L ranging codesare assigned to the SS for the bandwidth request ranging process asdenoted by a prescribed term of “L RCs for BW-request ranging”. Theassigned ranging codes are transmitted to the SSs using the DL_MAPmessage, and the SSs perform necessary ranging procedures using theranging codes contained in the DL_MAP message.

[0023] The period ranging process is periodically executed such that anSS which has controlled a time offset between the SS and the BS and atransmission power in the initial ranging process can control a channelstate associated with the BS. The SS performs the period ranging processusing the ranging codes assigned for the period ranging process.

[0024] The bandwidth request ranging process enables the SS, which hascontrolled a time offset between the SS and the BS and a transmissionpower in the initial ranging process, to request a bandwidth allocationfrom the BS in such a way that the SS can communicate with the BS.

[0025] Referring to FIG. 3, the uplink frame includes an initialmaintenance opportunity field 300 using the initial and period rangingprocesses, a request contention opportunity field 310 using thebandwidth request ranging process, and an SS scheduled data field 320including uplink data of a plurality of SSs. The initial maintenanceopportunity field 300 includes a plurality of access burst fields eachhaving initial and period ranging processes, and a collision field inwhich there is a collision between the access burst fields. The requestcontention opportunity field 310 includes a plurality of bandwidthrequest fields each having a real bandwidth request ranging process, anda collision field in which there is a collision between the bandwidthrequest ranging fields. The SS scheduled data fields 320 each include aplurality of SS scheduled data fields (i.e., SS 1 scheduled datafield˜SS N scheduled data field). The SS transition gap is positionedbetween the SS scheduled data fields (i.e., SS 1 scheduled data field˜SSN scheduled data field).

[0026] The UIUC (Uplink Interval Usage Code) area records informationidentifying the usage of offsets recorded in the offset area. Forexample, provided that 2 is recorded in the UIUC area, a starting offsetfor use in the initial ranging process is recorded in the offset area.When 3 is recorded in the UIUC area, a starting offset for use in eitherthe bandwidth request ranging or the maintenance ranging process isrecorded in the offset area. The offset area records a starting offsetvalue for use in either the initial ranging process or the maintenanceranging process according to the information recorded in the UIUC area.Physical channel characteristic information to be transferred from theUIUC area is recorded in the UCD.

[0027] As described above, the IEEE 802.16a communication system hasconsidered a fixed state of a current SS (i.e., there is noconsideration given to the mobility of the SS) and a single cellstructure. However, the IEEE 802.16e communication system has beendefined as a system for considering the SS's mobility in the IEEE802.16a communication system, such that the IEEE 802.16e communicationsystem must consider the SS's mobility in a multi-cell environment. Inorder to provide the SS's mobility in the multi-cell environment,individual operations modes of the SS and the BS must be converted. Morespecifically, many developers have conducted intensive research into anSS handover system considering a multi-cell structure to provide theSS's mobility.

[0028] As such, in order to enable the IEEE 802.16e communication systemto support a handover function, the SS must measure SINRs of pilotsignals transferred from neighbor BSs and an active BS to which the SScurrently belong. When the SINR of the pilot signal transferred from theactive BS is lower than SINRs of pilot signals transferred from theneighbor BSs, the SS transmits a handover request to the active BS. Amethod for controlling a mobile SS to measure the SINRs of the pilotsignals transferred from the active BS and the neighbor BSs in the IEEE802.16e communication system will be described later in more detail withreference to FIG. 4. In this case, the expression “Pilot signal's SINRmeasurement” is called a “Pilot signal's SINR scan or scanning” for theconvenience of description. It should be noted that the term “Scan” issubstantially equal to the other term “Scanning”.

[0029]FIG. 4 is a flow chart illustrating a method for measuring SINRsof pilot signals transferred from the active BS and the neighbor BSs ina broadband wireless access communication system for use with aconventional OFDM/OFDMA scheme. More specifically, the method formeasuring SINRs of pilot signals transferred from the active BS and theneighbor BSs in the IEEE 802.16e communication system is illustrated inFIG. 4.

[0030] However, prior to describing FIG. 4, as indicated above, the IEEE802.16e communication system considers the mobility of SSs in the IEEE802.16a communication system. The SS with the mobility in the IEEE802.16e communication system is called an MSS (Mobile SubscriberStation).

[0031] Referring to FIG. 4, the BS 450 transmits an NBR_ADV (NeighborBSs Advertisement) message to the MSS 400 at step 411. The detailedconfiguration of the NBR_ADV message is shown in Table 4 below. TABLE 4Syntax Size Notes NBR_ADV Message_Format( ){  Management Message Type=? 8 bits  N_NEIGHBORS  8 bits  For(i=0;j<N_NEIGHBORS;j++){   NeighborBS-ID 48 bits   Configuration Change Count  8 bits   Physical Frequency16 bits   TLV Encoded Neighbor Information Variable TLV specific  } }

[0032] Referring to Table 4, the NBR_ADV message includes a ManagementMessage Type field including transmission message type information; anN_NEIGHBORS field including the number of neighbor BSs; a neighbor BS-IDfield including ID information of the neighbor BSs; a ConfigurationChange Count field including the number of configuration changes; aphysical frequency field including physical channel frequencies of theneighbor BSs; and a TLV (Type/Length/Value) Encoded Neighbor Informationfield including other information associated with neighbor BSs otherthan the above described information. It should be noted that theManagement Message Type field to which the NBR_ADV message will betransmitted is currently in an undecided state, as denoted by“Management Message Type=? (undecided)”.

[0033] The MSS 400 that is receiving the NBR_ADV message transmits aSCAN_REQ (Scan Request) message to the BS 450 when it wishes to scanSINRs of pilot signals transferred from the neighbor BSs at step 413. Inthis case, the time at which the MSS 400 generates a scan request is notdirectly associated with the pilot SINR scanning operation, such thatits detailed description will herein be omitted.

[0034] The SCAN_REQ message configuration is shown in Table 5 below.TABLE 5 Syntax Size Notes SCN_REQ Message_Format( ){  Management MessageType=?  8 bits  Scan Duration 20 bits For SCa PHY, units are mini-slots.For OFDM/OFDMA PHY, units are OFDM symbols }

[0035] Referring to Table 5, the SCAN_REQ message includes a ManagementMessage Type field including a plurality of IEs (i.e., transmissionmessage type information), and a Scan Duration field including ascan-desired scan duration for SINRs of pilot signals transferred fromthe neighbor BSs. If the IEEE 802.16e communication system is a systemfor use with a Single Carrier (SC), i.e., if the scan duration field isapplied to an SC physical channel, the scan duration field is configuredin units of mini-slots. If the IEEE 802.16e system acts as theOFDM/OFDMA system, i.e., if the IEEE 802.16e system is applied to theOFDM/OFDMA physical channel, it is configured in the form of OFDM-symbolunits. It should be noted that the Management Message Type field towhich the SCAN_REQ message will be transmitted is currently in anundecided state, as denoted by “Management Message Type=? (undecided)”.

[0036] The BS 450 receiving the SCAN_REQ message transmits a DL_MAPmessage including information to be scanned by the MSS 400 to the MSS400 at step 415. In this case, the SCANNING_IE message including scaninformation contained in the DL_MAP message is shown in Tables 6, 7, and8 below. TABLE 6 For SCa PHY: Syntax Size Notes Scanning_IE {  CID 16bits MSS basic CID  Scan Start 22 bits Offset (in units of mini-slots)to the start of the scanning interval from the mini-slot boundaryspecified by the downlink Allocation_Start_Time  Scan Duration 22 bitsDuration (in units of mini-slots) where the MSS may scan for neighbor BS}

[0037] Referring to Table 6, the SCANNING_IE message includes scaninformation for use in the SC physical channel. Parameters contained inthe SCANNING_IE message are a CID (Connection ID), a Scan Start value,and a scan duration value. The CID includes an MSS basic CID for usewith the SCANNING_IE message. The Scan Start value is a predeterminedtime at which the MSS begins a pilot SINR scanning operation. The scanduration is a predetermined interval during which the MSS performs thepilot SINR scanning operation. The scan start and scan duration valuesfor use in the SC physical channel are configured in the form ofmini-slot units. TABLE 7 For OFDM PHY: Syntax Size Notes Scanning_IE { CID 16 bits MSS basic CID  Scan Start 18 bits Indicate the scanninginterval start time, in units of OFDM symbol duration, relative to thestart of the first symbol of the PHY PDU (including preamble) where theDL_MAP message is transmitted  Scan Duration 18 bits Duration (in unitsof OFDM symbols) where the MSS may scan for neighbor BS }

[0038] Referring to Table 7, the SCANNING_IE message includes scaninformation for use in the OFDM physical channel. Parameters containedin the SCANNIG_IE message are a CID (Connection ID), a Scan Start value,and a scan duration value. The CID indicates an MSS basic CID for usewith the SCANNING_IE message. The Scan Start value is a predeterminedtime at which the MSS begins a pilot SINR scanning operation. The scanduration is a predetermined interval during which the MSS performs thepilot SMIR scanning operation. The scan start and scan duration valuesfor use in the OFDM physical channel are configured in the form ofOFDM-symbol units. TABLE 8 For OFDM PHY: Syntax Size Notes Scanning_IE { CID 16 bits MSS basic CID  Scan Start 18 bits The offset of the OFDMsymbol in which the scanning interval starts. Measured in OFDM symbolsfrom the time specified by the Allocation_Start_time_Field in the DL_MAP Scan Duration 18 bits Duration (in units of OFDM symbols) where the MSSmay scan for neighbor BS }

[0039] Referring to Table 8, the SCANNING_IE message includes scaninformation for use in the OFDMA physical channel. Parameters containedin the SCANNIG_IE message are a CID (Connection ID), a Scan Start value,and a scan duration value. The CID includes an MSS basic CID for usewith the SCANNING_IE message. The Scan Start value is a predeterminedtime at which the MSS begins a pilot SINR scanning operation. The scanduration is a predetermined interval during which the MSS performs thepilot SINR scanning operation. The scan start and scan duration valuesfor use in the OFDM physical channel are configured in the form ofOFDM-symbol units.

[0040] The MSS 400, having received the DL_MAP message including thescanning_IE message, scans pilot SINRs associated with neighbor BSsrecognized by the NBR_ADV message according to parameters contained inthe SCANNING_IE message at step 417. It should be noted that SINRs ofpilot signals transferred from the neighbor BSs and the SINR of thepilot signal transferred from the BS 450 to which the MSS 400 currentlybelongs are continuously scanned, even though it is not illustrated inFIG. 4.

[0041]FIG. 5 is a flow chart illustrating a handover request process ofan MSS in a broadband wireless access communication system for use witha conventional OFDM/OFDMA scheme. More specifically, an MSS handoverrequest process for use in the IEEE 802.16e communication system isillustrated in FIG. 5.

[0042] Referring to FIG. 5, the BS 550 transmits an NBR_ADV message tothe MSS 500 at step 511. The MSS 500, having received the NBR_ADVmessage, transmits a SCAN_REQ message to the BS 550 when it wishes toscan SINRs of pilot signals transferred from the neighbor BSs at step513. In this case, the time at which the MSS 500 generates a scanrequest is not directly associated with the pilot SINR scanningoperation, such that its detailed description will herein be omitted.The BS 550, having received the SCAN_REQ message, transmits a DL_MAPmessage including the SCANNING_IE message (i.e., information to bescanned by the MSS 500) to the MSS 500 at step 515. In association withthe neighbor BSs recognized by the NBR_ADV message, the MSS 500, havingreceived the DL_MAP message including the SCANNING_IE message, scansSINRs of pilot signals in response to parameters (i.e., a scan startvalue and a scan duration) contained in the SCANNING_IE message at step517. It should be noted that SINRs of pilot signals transferred from theneighbor BSs and the SINR of the pilot signal transferred from the BS550 to which the MSS 500 currently belongs are continuously scanned,even though it is not illustrated in FIG. 5.

[0043] If it is determined that the MSS 500 must change its currentactive BS to another BS at step 519, after the scanning operations ofthe SINRs of pilot signals received from the neighbor BSs have beencompleted, i.e., if it is determined that the MSS 500 must change itscurrent active BS to a new BS, the MSS 500 transmits an MSSHO_REQ(Mobile Subscriber Station HandOver Request) message to the BS 550 atstep 521. The MSSHO_REQ message configuration is shown in Table 9 below.TABLE 9 Syntax Size Notes MSSHO_REQ Message_Format( ){  ManagementMessage Type=?  8 bits  Estimated HO time  8 bits  N_Recommended  8 bits For(i=0;j<N_NEIGHBORS;j++){   Neighbor BS-ID 48 bits   BS S/(N+I)  8bits  } }

[0044] Referring to Table 9, the MSSHO_REQ message includes a ManagementMessage Type field identifying a plurality of IEs (i.e., transmissionmessage type information), an estimated HO time field including ahandover start time, and an N_Recommended field including the scanningresult of the MSS. In this case, the N_Recommended field includes IDinformation of neighbor BSs and SINR information of pilot signals of theneighbor BSs. It should be noted that the Management Message Type fieldto which the MSSHO_REQ message will be transmitted is currently in anundecided state, as denoted by “Management Message Type=? (undecided)”.

[0045] After transmitting the MSSHO_REQ message to the BS 550, the MSS500 re-scans SINRs of pilot signals in association with the neighbor BSsat step 523.

[0046] First and second problems of the MSS scanning operation for usein the IEEE 802.16e communication system will now be described hereinbelow.

[0047] In the first problem, although the MSS scans pilot SINRs ofneighbor BSs in response to the scanning information received from theactive BS, there is no procedure for additionally reporting the pilotSINR scanning result of the active BS and neighbor BSs. In the secondproblem, there is no procedure for enabling the MSS to scan pilot SINRsof neighbor BSs before the MSS transmits a scan request to the activeBS.

[0048] In order to enable the IEEE 802.16e communication system tosupport a handover function of the MSS, a handover function of a mobilesubscriber must be made available upon receipt of a request signal fromthe MSS and a request signal from the BS. In order to enhance systemefficiency, it is desirable that the BS continues to manage the pilotSINR scanning state (i.e., the MSS state) after the MSS has been poweredon. However, the IEEE 802.16e communication system cannot report an MSShandover procedure and an MSS pilot SINR scanning state upon receiving arequest signal from the BS, such that there must be newly developed suchprocedures for reporting the MSS handover procedure and the MSS pilotSINR scanning state.

SUMMARY OF THE INVENTION

[0049] Accordingly, the present invention has been designed in view ofthe above and other problems, and it is an object of the presentinvention to provide a method for measuring and reporting a channelquality in a broadband wireless access communication system.

[0050] It is another object of the present invention to provide a methodfor measuring a channel quality in a broadband wireless accesscommunication system even though there is no additional request from amobile subscriber.

[0051] It is yet another object of the present invention to provide amethod for performing a handover function in response to a channelquality in a broadband wireless access communication system.

[0052] In accordance with one aspect of the present invention, the aboveand other objects are accomplished by a method for measuring channelqualities of an active BS (Base Station) and neighbor BSs when an MSS(Mobile Subscriber Station) is located in an area covered by the activeBS and neighbor BSs in a communication system including the MSS (MobileSubscriber Station), the active BS for providing the MSS with a desiredservice, and a plurality of BSs adjacent to the active BS, comprisingthe steps of: a) controlling the active BS to transmit channel qualitymeasurement information needed for the MSS to measure channel qualitiesof the active BS and neighbor BSs to the MSS; b) controlling the activeBS to transmit channel quality measurement information, and transmittingneighbor BS-associated information indicative of information associatedwith the neighbor BSs to the MSS; and c) controlling the MSS to measurea channel quality according to the channel quality measurementinformation in association with the active BS and the neighbor BSsassociated with the neighbor BS-associated information.

[0053] In accordance with another aspect of the present invention, thereis provided a method for reporting channel qualities of an active BS(Base Station) and neighbor BSs measured by an MSS (Mobile SubscriberStation) to the active BS when the MSS is located in an area covered bythe active BS and the neighbor BSs in a communication system includingthe MSS (Mobile Subscriber Station), the active BS for providing the MSSwith a desired service, and the plurality of BSs adjacent to the activeBS, comprising the steps of: a) controlling the active BS to transmitchannel quality measurement information needed for the MSS to measurechannel qualities of the active BS and the neighbor BSs and also otherchannel quality report information needed to report the channelqualities of the measured active BS and the neighbor BSs to the MSS; b)controlling the MSS to measure a channel quality according to thechannel quality measurement information in association with the activeBS and the neighbor BSs associated with neighbor BS-associatedinformation; and c) controlling the MSS to transmit the channelqualities of the measured active BS and neighbor BSs to the active BSaccording to the channel quality report information.

[0054] In accordance with yet another aspect of the present invention,there is provided a method for reporting channel qualities of active BS(Base Station) and neighbor BSs measured by an MSS (Mobile SubscriberStation) to the active BS when the MSS is located in an area covered bythe active BS and the neighbor BSs in a communication system includingthe MSS (Mobile Subscriber Station), the active BS for providing the MSSwith a desired service, and the plurality of BSs adjacent to the activeBS, comprising the steps of: a) controlling the active BS to transmitchannel quality measurement information needed for the MSS to measurechannel qualities of the active BS and neighbor BSs, and also otherchannel quality report information needed to report the channelqualities of the measured active BS and the measured neighbor BSs to theMSS; b) controlling the MSS to measure a channel quality according tothe channel quality measurement information in association with theactive BS and the neighbor BSs associated with neighbor BS-associatedinformation; c) controlling the MSS to transmit the channel qualities ofthe measured active BS and the measured neighbor BSs to the active BS;d) controlling the MSS to measure channel qualities of the active BS andthe neighbor BSs according to the channel quality measurementinformation; and e) controlling the MSS to transmit individual channelqualities of the measured active NS and neighbor BSs in response to thechannel quality report information to the active BS.

[0055] In accordance with yet another aspect of the present invention,there is provided a method for reporting channel qualities of active BS(Base Station) and neighbor BSs measured by an MSS (Mobile SubscriberStation) to the active BS when the MSS is located in an area covered bythe active BS and the neighbor BSs in a communication system includingthe MSS (Mobile Subscriber Station), the active BS for providing the MSSwith a desired service, and the plurality of BSs adjacent to the activeBS, comprising the steps of: a) receiving channel quality reportinformation identifying channel periods of the channel qualities fromthe active BS, and receiving channel quality measurement informationassociated with individual channel qualities of the neighbor BSs and theactive BS from the active BS; b) measuring SINRs (Signal to Interferenceand Noise Ratios) of the neighbor BSs and the active BS according to thechannel quality measurement information; and c) reporting the measuredSINRs of the neighbor BSs and the active BS to the active BS accordingto the channel quality report period.

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The above and other objects, features, and advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

[0057]FIG. 1 is a block diagram illustrating a broadband wireless accesscommunication system using an OFDM/OFDMA scheme;

[0058]FIG. 2 is a conceptual diagram illustrating a downlink framestructure for use in a broadband wireless access communication systemusing an OFDM/OFDMA scheme;

[0059]FIG. 3 is a conceptual diagram illustrating an uplink framestructure for use in a broadband wireless access communication systemusing an OFDM/OFDMA scheme;

[0060]FIG. 4 is a flow chart illustrating a method for measuring SINRsof pilot signals transferred from active BS and neighbor BSs in abroadband wireless access communication system using an OFDM/OFDMAscheme;

[0061]FIG. 5 is a flow chart illustrating a handover request process ofan MSS in a broadband wireless access communication system using anOFDM/OFDMA scheme;

[0062]FIG. 6 is a block diagram illustrating a broadband wireless accesscommunication system using an OFDM/OFDMA scheme in accordance with thepresent invention;

[0063]FIG. 7 is a flow chart illustrating a pilot SINR scanningprocedure in accordance with a first preferred embodiment of the presentinvention;

[0064]FIG. 8 is a flow chart illustrating a pilot SINR scanningprocedure in accordance with a second preferred embodiment of thepresent invention;

[0065]FIG. 9 is a flow chart illustrating a pilot SINR scan reportprocedure in accordance with a third preferred embodiment of the presentinvention;

[0066]FIG. 10 is a flow chart illustrating a pilot SINR scan reportprocedure in accordance with a fourth preferred embodiment of thepresent invention; and

[0067]FIG. 11 is a flow chart illustrating a pilot SINR scan reportprocedure in accordance with a fifth preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0068] Preferred embodiments of the present invention will be describedin detail herein below with reference to the annexed drawings. In thedrawings, the same or similar elements are denoted by the same referencenumerals even though they are depicted in different drawings. In thefollowing description, a detailed description of known functions andconfigurations incorporated herein will be omitted when it may make thesubject matter of the present invention rather unclear.

[0069] Prior to describing the present invention, the handover procedureproposed by the current IEEE 802.16e system includes only twoprocedures, i.e., a scanning procedure and an SINR scanning resultreport procedure. More specifically, the scanning procedure is used tomeasure an SINR of a pilot signal upon receipt of an MSS request, andthe SINR scanning result report procedure is used to report the SINRscanning result of a pilot signal upon receiving a handover request froman MSS. In this case, the expression “Pilot signal's SINR measurement”is considered to be the same as the other expression “Pilot signal'sSINR scan or scanning” for the convenience of description. It should benoted that the term “Scan” is substantially equal to the term“Scanning”. However, in order to provide the MSS with an effectivehandover operation, the MSS must conduct pilot SINR scanning operationsof neighbor BSs before generating a handover request. Where an active BSfor providing the MSS with a desired service is changed to another BSdue to movement of the MSS, the MSS must continuously conduct pilot SINRscanning operations of the active BS and the neighbor BSs, and mustinform the active BS of the scanning pilot SINR results, such that ahandover function for the changed active BS is performed. In order toimplement an effective handover operation of the MSS, the presentinvention provides a method for performing a pilot SINR scanningoperation upon receiving a control signal from a BS without using arequest signal of the MSS, and a method for controlling the MSS toreport the scanned pilot SINR results.

[0070]FIG. 6 is a block diagram illustrating a broadband wireless accesscommunication system using an OFDM/OFDMA scheme in accordance with thepresent invention. However, prior to describing the BWA communicationsystem illustrated in FIG. 6, it should be noted that the IEEE 802.16ecommunication system acting as a communication system for consideringthe SS's mobility in the EEE 802.16a communication system has not beendeveloped yet. Provided that the SS's mobility is considered in the IEEE802.16a communication system, it is possible to consider the multi-cellstructure and an SS's handover operation between the multi-cells.Therefore, the present invention provides the IEEE 802.16e communicationsystem as illustrated in FIG. 6. The present invention utilizes the IEEE802.16e communication system as a BWA (Broadband Wireless Access)communication system using an OFDM/OFDMA scheme as a representativeexample. Accordingly, it should be noted that an SC (Single Carrier)scheme is applicable to the IEEE 802.16e communication system. In thiscase, the pilot signal's SINR indicates a channel quality of a specificchannel established between the MSS and the BS.

[0071] Referring to FIG. 6, the IEEE 802.16e communication systemincludes a multi-cell structure, i.e., a plurality of cells 600 and 650.More specifically, the IEEE 802.16e communication system includes afirst BS 610 for managing the cell 600, a second BS 640 for managing thecell 650, and a plurality of MSSs 611, 613, 630, 651, and 653. Signaltransmission and reception among the BSs 610 and 640 and the MSSs 611,613, 630, 651, and 653 is established using the OFDM/OFDMA scheme. TheMSS 630 from among the MSSs 611, 613, 630, 651, and 653 is positioned ina boundary (i.e., a handover area) between the first cell 600 and thesecond cell 650. The IEEE 802.16e communication system can provide theMSS's mobility on the condition that the handover operation for the MSS630 must be supported.

[0072]FIG. 7 is a flow chart illustrating a pilot SINR scanningprocedure in accordance with a first preferred embodiment of the presentinvention. Referring to FIG. 7, the BS 750 transmits a DL(DownLink)_MAPmessage to the MSS 700 at step 711. In this case, the DL_MAP messageincludes a SCANNING_IE (Information Element) message identifying scaninformation of the MSS 700 in a conventional DL_MAP message of the IEEE802.16e system described in the prior art. More specifically, if thepowered-on MSS 700 is initialized to control the MSS 700 to perform theSINR scanning operation, the BS 750 includes the SCANNING_IE message inthe DL_MAP message, and transmits the SCANNING_IE message including theDL_MAP message to the MSS 700 without receiving a scan request signalfrom the MSS 700. In this case, the SCANNING_IE message may be equal tothe SCANNING_IE messages shown in Tables 6 to 8 of the prior art, or mayalso be equal to a new SCANNING_IE message of the present invention. TheSCANNING_IE message acts as channel quality measurement information formeasuring the pilot SINR (i.e., a channel quality). The new SCANNING_IEmessages of the present invention are shown in Tables 10 to 12 below.TABLE 10 For SCa PHY: Syntax Size Notes Scanning_IE {  CID 16 bits MSSbasic CID  Scan Start 22 bits Offset (in units of mini-slots) to thestart of the scanning interval from the mini-slot boundary specified bythe downlink Allocation_Start_Time  Scan Duration 22 bits Duration (inunits of mini-slots) where the MSS may scan for neighbor BS  Scan Period22 bits Period (in units of mini-slots) when the MSS may scan forneighbor BS }

[0073] Referring to Table 10, the SCANNING_IE message includes scaninformation for use in the SC physical channel. Parameters contained inthe SCANNIG_IE message are a CID (Connection ID), a Scan Start value, aScan Duration value, and a Scan Period value. The CID identifies an MSSbasic CID for use with the SCANNING_IE message. The Scan Start value isa predetermined time at which the MSS begins a pilot SINR scanningoperation. The Scan Duration is a predetermined interval during whichthe MSS performs the pilot SINR scanning operation. The scan period is apredetermined period during which the MSS performs the pilot SINR scanoperation. The scan start value, the scan duration value, and the scanperiod value for use in the SC physical channel are configured in theform of mini-slot units. TABLE 11 For OFDM PHY: Syntax Size NotesScanning_IE {  CID 16 bits MSS basic CID  Scan Start 18 bits Indicatethe scanning interval start time, in units of OFDM symbol duration,relative to the start of the first symbol of the PHY PDU (includingpreamble) where the DL_MAP message is transmitted  Scan Duration 18 bitsDuration (in units of OFDM symbols) where the MSS may scan for neighborBS  Scan Period 18 bits Period (in units of OFDM symbols) when the MSSmay scan for neighbor BS }

[0074] Referring to Table 11, the SCANNING_E message includes scaninformation for use in the OFDM physical channel. Parameters containedin the SCANNIG_IE message are a CID (Connection ID), a Scan Start value,a Scan Duration value, and a Scan Period value. The CID identifies anMSS basic CID for use with the SCANNING_IE message. The Scan Start valueis a predetermined time at which the MSS begins a pilot SINR scanningoperation. The scan duration is a predetermined interval during whichthe MSS performs the pilot SINR scanning operation. The scan period is apredetermined period during which the MSS performs the pilot SINR scanoperation. The scan start value, the scan duration value, and the scanperiod value for use in the OFDM physical channel are configured in theform of OFDM-symbol units. TABLE 12 For OFDMA PHY: Syntax Size NotesScanning_IE {  CID 16 bits MSS basic CID  Scan Start 18 bits The offsetof the OFDM symbol in which the scanning interval starts. Measured inOFDM symbols from the time specified by the Allocation_Start_time_Fieldin the DL_MAP  Scan Duration 18 bits Duration (in units of OFDM symbols)where the MSS may scan for neighbor BS  Scan Period 18 bits Period (inunits of OFDM symbols) when the MSS may scan for neighbor BS }

[0075] Referring to Table 12, the SCANNING_IE message includes scaninformation for use in the OFDMA physical channel. Parameters containedin the SCANNIG_IE message are a CID (Connection ID), a Scan Start value,and a scan duration value. The CID identifies an MSS basic CID for usewith the SCANNING_IE message. The Scan Start value is a predeterminedtime at which the MSS begins a pilot SINR scanning operation. The scanduration is a predetermined interval during which the MSS performs thepilot SINR scanning operation. The scan period is a predetermined periodduring which the MSS performs the pilot SINR scan operation. The scanstart value, the scan duration value, and the scan period value for usein the OFDM physical channel are configured in the form of OFDM-symbolunits.

[0076] The BS 750 transmits an NBR_ADV (Neighbor BSs Advertisement)message to the MSS 700. As previously stated in Table 4, the NBR_ADVmessage includes a Management Message Type field including transmissionmessage type information; an N_Neighbors field including the number ofneighbor BSs; a neighbor BS-ID field including ID information of theneighbor BSs; a Configuration Change Count field including the number ofconfiguration changes; a physical frequency field including physicalchannel frequencies of the neighbor BSs; and a TLV Encoded NeighborInformation field including information associated with the neighborBSs, other than the above neighbor-BSs-associated information.

[0077] The MSS 700, having received the NBR_ADV message including theinformation associated with the neighbor BSs from the BS 750, scansneighbor BSs recognized by the NBR_ADV message (i.e., SINRs of pilotsignals transferred from the neighbor BSs) according to parameterscontained in the SCANNING_IE message contained in the DL_MAP message atstep 715. It should be noted that SINRs of pilot signals transferredfrom the neighbor BSs and the SINR of the pilot signal transferred fromthe BS 750 to which the MSS 700 currently belongs are continuouslyscanned, even though it is not illustrated in FIG. 7.

[0078] As a result, in accordance with the MSS scanning procedureillustrated in FIG. 7, the BS transmits scan information associated withthe scanning operation to the MSS even though the MSS does not transmitan additional request to the BS, such that the MSS can effectivelyperform a scan operation.

[0079]FIG. 8 is a flow chart illustrating a pilot SJNR scanningprocedure in accordance with a second preferred embodiment of thepresent invention. However, prior to describing FIG. 8, the SJNRscanning process of the first preferred embodiment illustrated in FIG. 7is a pilot SINR scanning process of the MSS in response to the scaninformation of the BS. The SINR scanning process of the second preferredembodiment changes scan information such as scan duration and scanperiod information to other information upon receiving a request fromthe MSS while the MSS scans the pilot SINR in response to scaninformation transferred from the BS, such that the pilot SINR can bescanned.

[0080] Referring to FIG. 8, the BS 850 transmits a DL_MAP message to theMSS 800 at step 811. The DL_MAP message includes the SCANNING_IE messageincluding the MSS 800's scan information in the conventional DL_MAPmessage of the IEEE 802.16e communication system previously stated inthe prior art. In this case, the SCANNING_IE message may be the same asthe SCANNING_IE messages shown in Tables 6 to 8 of the prior art, or mayalso be equal to a new SCANNING_IE message of the present invention,i.e., the same SCANNING_IE message described in Tables 10 to 12.

[0081] After transmitting the DL_MAP message, the BS 850 transmits theNBR_ADV message to the MSS 800 at step 813. As previously stated inTable 4, the NBR_ADV message includes a Management Message Type fieldincluding transmission message type information (i.e., a plurality ofIEs); an N_Neighbors field including the number of neighbor BSs; aneighbor BS-ID field including ID information of the neighbor BSs; aConfiguration Change Count field including the number of configurationchanges; a physical frequency field including physical channelfrequencies of the neighbor BSs; and a TLV Encoded Neighbor Informationfield including information associated with the neighbor BSs other thanthe above neighbor-BSs-associated information.

[0082] The MSS 800, having received the NBR_ADV message including theinformation associated with the neighbor BSs from the BS 850, scansneighbor BSs recognized by the NBR_ADV message (i.e., SINRs of pilotsignals transferred from the neighbor BSs) according to parameterscontained in the SCANNING_IE message contained in the DL_MAP message atstep 815. It should be noted that SINRs of pilot signals transferredfrom the neighbor BSs and the SINR of the pilot signal transferred fromthe BS 850 to which the MSS 800 currently belongs are continuouslyscanned, even though it is not illustrated in FIG. 8.

[0083] As a result, the MSS decides to change scan-associatedinformation (i.e., scan information such as scan duration and scanperiod information) while scanning SINRs of the pilot signalstransferred from the neighbor BSs at step 817. In this case, there maybe a plurality of conditions for controlling the MSS 80 to changescan-associated information. For example, where the measurement periodmust be adjusted according to physical channel capacity, scanninginformation conversion may be requested. More specifically, if there istoo much load in the physical channel, the MSS 800 may determine ameasurement period to be a long measurement period. If there isrelatively little load in the physical channel, the MSS 800 maydetermine a measurement period to be a relatively short measurementperiod.

[0084] The MSS 800, having decided to change scanning information toother information, transmits a SCAN_REQ message to the BS 850 at step819. In this case, the SCAN_REQ message includes a Management MessageType field including transmission message type information (i.e., aplurality of IEs) and a Scan Duration field indicative of a desired scanduration during which the SINRs of the pilot signals transferred fromthe neighbor BSs will be scanned. If the IEEE 802.16e communicationsystem is based on an SC scheme, i.e., if the scan duration field isadapted to an SC physical channel, the scan duration field is configuredin the form of mini-slot units. If the IEEE 802.16e communication systemis an OFDM/OFDMA system, i.e., if the IEEE 802.16e communication systemis applied to an OFDM/OFDMA physical channel, the scan duration field isconfigured in the form of OFDM symbols.

[0085] The BS 850, having received the SCAN_REQ message, transmits theDL_MAP message including information to be scanned by the MSS 800 to theMSS 800 at step 821. The MSS 800 receives the DL_MAP message includingthe SCANNING_IE message and performs a pilot SINR scanning processassociated with the neighbor BSs in response to parameters contained inthe SCANNING_IE message at step 823.

[0086]FIG. 9 is a flow chart illustrating a pilot SINR scan reportprocedure in accordance with the third preferred embodiment of thepresent invention. However, prior to describing FIG. 9, it should benoted that a current IEEE 802.16e communication system has not proposedadditional procedures for controlling the MSS to report pilot SINR scanresult information. Because there is no process for reporting such pilotSINR scan result information in the IEEE 802.16e communication system,the BS may command the MSS to be handed over to another BS even thoughit does not recognize SINR scan result data associated with neighbor BSsof the MSS, resulting in deterioration of communication efficiency. Forexample, it is assumed that the neighbor BSs of the MSS are composed offirst to sixth BSs and an SINR value of a pilot signal received from thesecond BS is a maximum value. In this case, the MSS may have the bestchannel condition when it is handed over to the second BS from among sixneighbor BSs, but an active BS to which the MSS currently belongs doesnot recognize the SINR scan result data of the neighbor BSs. The MSS mayalso be handed over to another BS (e.g., the sixth BS) different fromthe second BS. The BS can transmit a handover request signal to the MSSin the following two cases.

[0087] The first case indicates a specific case where the current BS'scapacity reaches a threshold value. The second case indicates a specificcase where an MSS having a priority higher than that of the currentservice MSS enters the BS.

[0088] Due to the aforementioned reasons, it is very important for theMSS to report pilot SINR scanning result data. The present inventionproposes two pilot SINR scanning result report methods, i.e., a periodicscan report method and an event triggering scan report method. Theperiodic scan report method and the event trigger scan report methodwill hereinafter be described in more detail.

[0089] (1) Periodic Scan Report Method

[0090] In accordance with the periodic scan report method, the MSSreports SINRs of pilot signals of the scanned active BS and neighbor BSsto the active BS according to a predetermined period.

[0091] (2) Event Triggering Scan Report Method

[0092] In accordance with the event triggering scan report method, theMSS reports SINRs of pilot signals of the scanned active BS and neighborBSs to the active BS only when prescribed setup events have beengenerated. The event triggering scan report method controls the MSS toreport SINRs of pilot signals of the scanned active BS and neighbor BSsto the active BS only when either one of events “a” and “b” has beengenerated. The event “a” and the other event “b” are shown in Table 13below. TABLE 13 Event Condition Operation Event When active BS is Whenevent “a” occurs after a unchanged but the order transmitting initialmeasurement, of neighbor BSs' SINRs pilot SINR measurement of neighboris changed BS is transmitted to serving BS via Scan_Report message EventWhen neighbor BS's When event “b” occurs, MSS b pilot SINR is higherthan transmits MSSHO_REQ message with serving BS's SINR neighbor BS'spilot SINR value to request handover function to serving BS

[0093] Referring to Table 13, the event “a” indicates a specific casewhen a pilot SINR of an active BS is not less than pilot SINRs ofneighbor BSs, but the magnitudes of the pilot SINRs of neighbor BSs arechanged, such that the order of the magnitudes is changed to anotherorder. More specifically, the event “a” indicates a specific case whenthe magnitudes of pilot SINRs of neighbor BSs are changed to others onthe condition that the active BS of the MSS is unchanged. The scanreport operations in case of generating the event “a” will hereinafterbe described. Before generating the event “a”, the MSS reportsinitially-scanned pilot SINRs of the active BS and neighbor BSs to theactive BS. When generating the event “a” while scanning the pilot SINRs,the scanned pilot SINRs of the active BS and neighbor BSs are reportedto the active BS. The scan report operation for the event “a” enablesthe active BS to continuously recognize the pilot SINRs of the neighborBSs in the same manner as in the periodic scan report method. Further,the scan report operation for the event “a” reduces the number of scanreport operations of the MSS as compared to the periodic scan reportoperation when the MSS moves to another position at a relatively lowspeed, such that it minimizes the amount of resource use in response tothe scan report operation, resulting in increased overall efficiency ofsystem resources. In this case, the scan report operation is carried outusing a SCAN_REPORT message, which will be described later in moredetail, such that its detailed description will herein be omitted.

[0094] Referring to Table 13, the event “b” indicates a specific casewhere there arises a neighbor BS with a pilot SINR magnitude higher thana pilot SINR magnitude of an active BS to which the MSS currentlybelongs. More specifically, the event “b” indicates a specific casewhere the active BS of the MSS is changed to another BS.

[0095] Before generating the event “b”, the MSS reportsinitially-scanned pilot SINRs of the active BS and neighbor BSs to theactive BS. Thereafter, in the case of generating the event “b”, the MSStransmits an MSSHO_REQ (Mobile Subscriber Station HandOver Request)message containing scanning result data of the active BS and neighborBSs to the active BS, such that it can request such a handover functionfrom the active BS. As previously shown in Table 9 of the prior art, theMSSHO_REQ message includes a Management Message Type field includingtransmission message type information (i.e., a plurality of IEs), anEstimated_Ho_Time field including a handover start time, and anN_Recommended field including MSS scanning result data. In this case,the N_Recommended field includes IDs of the neighbor BSs and SINRs ofpilot signals of the neighbor BSs. Therefore, the scan report operationfor the event “b” performs a scan report operation only when the MSSgenerates its request signal, such that it reduces the number of scanreport operations of the MSS as compared to the periodic scan reportoperation, such that it minimizes the amount of resource use in responseto the scan report operation, resulting in an increased overallefficiency of system resources.

[0096] It is assumed that the scan report method could be applied inFIG. 9. Referring to FIG. 9, the BS 950 transmits a DL_MAP message tothe MSS 900 at step 911. In this case, the DL_MAP message includes aSCAN_REPORT_IE message for implementing a scan report operation. In thiscase, the SCAN_REPORT_IE message acts as channel quality reportinformation for reporting a channel quality. The SCAN_REPORT_IE messageis shown in Table 14 below. TABLE 14 Syntax Size Notes Scan_Report_IE { CID 16 bits MSS basic CID  PERIODIC_N_REPORTMODE  8 bits PeriodicReport Mode number  For(i=0;j<PERIODIC_N_(—) REPORTMODE;j++){   ReportPeriod  8 bits Only if report Mode number  }  Event A mode  1 bit 0:Event A not used 1: Event A used  Event B mode  1 bit 0: Event B notused 1: Event B used  If (Event B mode == 1)   Timer 1  8 bits Only ifreport mode is event b. Timer 1 is the shortest time to maintain thesituation that pilot SINR of certain neighbor BS is higher than pilotSINR of serving BS  } }

[0097] Referring to Table 14, the SCAN_REPORT_IE message includes anN_REPORTMODE parameter. The N_REPORTMODE parameter indicates that thereare N report modes for the scan report function.

[0098] The present invention will hereinafter disclose three modes,i.e., a periodic report mode in response to a periodic scan reportoperation, an Event “a” mode in response to a scan report operation foroccurrence of the Event “a”, and an Event “b” mode in response to a scanreport operation for occurrence of the Event “b”. The present inventionmay carry out a scan report operation using either the event “a” mode orthe event “b” mode along with the periodic report mode, such that theMSS can periodically report pilot SINRs of the active BS and neighborBSs and can also perform an optimum scan report operation according tothe MSS moving situation.

[0099] The SCAN_REPORT_IE message shown in Table 14 includes aPERIODIC_N_REPORTMODE parameter. The PERIODIC_N_REPORTMODE parameterindicates the number of periodic scan report operations of the MSS. Inthis case, the scan report period may be variably determined, such thata Report Period value acting as the scan report period is marked on thePERIODIC_N_REPORTMODE parameter. An event is applied to the scan reportoperation on a one by one basis, the SCAN_REPORT_IE message includesEvent A mode- and Event B mode-parameters indicating which one of theevents is associated with a corresponding event triggering scan reportoperation.

[0100] The scan report operation for the Event “b” occurs in the casewhere pilot SINRs of neighbor BSs are higher than a pilot SINR of theactive BS. In this case, it is desirable that the MSSHO_REQ message betransmitted to the active BS only when the pilot SINRs of the neighborBSs are continuously higher than the pilot SINR of the active BS duringa predetermined time, because there may arise a ping-pong phenomenonwhen the active BS's pilot SINR and the pilot SINRs of the neighbor BSsare continuously changed to others. In this case, a timer for waitingfor a predetermined time to prevent the ping-pong phenomenon is called afirst timer (i.e., timer 1). The timer 1 is associated with only aspecific case in which the scan report operation occurs in response tothe event “b”. The DL_MAP message includes the SCANNING_IE message forscanning the MSS 900, and the SCANNING_IE message is shown above inTables 10 to 12.

[0101] Referring to FIG. 9, after transmitting a DL_MAP messageincluding the SCAN_REPORT IE and SCANNING_IE messages at step 911, theBS 950 transmits an NBR_ADV message to the MSS 900 at step 913. Aspreviously shown in Table 4, the NBR_ADV message includes a ManagementMessage Type field including transmission message type information(i.e., a plurality of IEs); an N_Neighbors field including the number ofneighbor BSs; a neighbor BS-ID field including ID information of theneighbor BSs; a Configuration Change Count field including the number ofconfiguration changes; a physical frequency field including physicalchannel frequencies of the neighbor BSs; and a TLV Encoded NeighborInformation field including information associated with the neighborBSs, other than the above neighbor-BSs-associated information.

[0102] The MSS 900 receives the NBR_ADV message including theinformation associated with the neighbor BSs from the BS 950 and scansneighbor BSs recognized by the NBR_ADV message (i.e., SINRs of pilotsignals transferred from the neighbor BSs) according to parameterscontained in the SCANNING_IE message contained in the DL_MAP message atstep 915. It should be noted that SINRs of pilot signals transferredfrom the neighbor BSs and the SINR of the pilot signal transferred fromthe BS 950 to which the MSS 900 currently belongs are continuouslyscanned, even though it is not illustrated in FIG. 9.

[0103] Accordingly, if a current time reaches a time periodcorresponding to the Report Period message of the SCAN_REPORT_IE messagecontained in the DL_MAP message at step 917, the MSS transmits theSCAN_REPORT message having pilot SINRs of the scanned neighbor BSs tothe BS 950 at step 919. The SCAN_REPORT message is shown in Table 15below. TABLE 15 Syntax Size Notes SCAN_REPORT_Message_Format ( ) { Management Message Type = ?  8 bits  Report Mode  2 bits 00: Periodic01: event a 10: event b  N_NEIGHBORS  8 bits For(i=0;j<N_NEIGHBORS;j++){   Neighbor BS-ID 48 bits   S(I+N) 16 bits } }

[0104] Referring to Table 15, the SCAN_REPORT message includes aManagement Message Type field indicating transmission message typeinformation (i.e., a plurality of IEs), a Report Mode field including areport mode, an N_Neighbors field including the MSS scanning result.Neighbor BS-IDs of neighbor BSs and pilot SINRs of individual neighborBSs are marked in the N_Neighbors field. In this case, the Report Modeindicates which mode is adapted to transmit the SCAN_REPORT message.

[0105] As described above, where the MSS performs the scan reportoperation simultaneously with transmitting a handover request, IEscontained in the SCAN_REPORT message are contained in the MSSHO_REQmessage without any change. The associated operations of the MSS will bedescribed later in more detail.

[0106] The MSS 900 transmits the SCAN_REPORT message to the BS 950, andscans pilot SINRs of neighbor BSs in response to parameters contained inthe SCANNING_IE message at step 921. If a current time reaches a timeperiod corresponding to the Report Period message of the SCAN_REPORT_IEmessage during the scanning times of the SINRs of the pilot signalstransmitted from the neighbor BSs at step 923, the MSS transmits theSCAN_REPORT message including pilot SINRs of the scanned neighbor BSs tothe BS 950 at step 925. The MSS 900 transmits the SCAN_REPORT message tothe BS 950, and re-scans pilot SINRs of neighbor BSs in response toparameters contained in the SCANNING_IE message at step 927. Therefore,the MSS 900 can periodically report pilot SINRs of the active BS andneighbor BSs to the BS 950.

[0107]FIG. 10 is a flow chart illustrating a pilot SINR scan reportprocedure in accordance with a fourth preferred embodiment of thepresent invention. It is assumed that the scan report method utilizesthe scan report method based on the event “a” occurrence in FIG. 10.

[0108] Referring to FIG. 10, the BS 1050 transmits a DL_MAP messageincluding the SCAN_REPORT_IE message to the MSS 1000 at step 1011. TheSCAN_REPORT_IE message includes the same parameters as in Table 14. Thescan report method is based on the occurrence of the event “a”, suchthat the Event “a” mode value is determined to be a value of 1. TheDL_MAP message also includes the SCANNING_IE message for the MSS 1000'sscanning operation, and the SCANNING_IE message is shown in Tables 10 to12.

[0109] The BS 1050 transmits the DL_MAP message including theSCAN_REPORT_IE and SCANNING_IE messages to the MSS 1000, and transmitsthe NBR_ADV message to the MSS 1000 at step 1013. The NBR_ADV message isthe same as in Table 4 of the prior art, such that its detaileddescription will herein be omitted.

[0110] The MSS 1000, having received the NBR_ADV message including theinformation associated with the neighbor BSs from the BS 1050, scansneighbor BSs recognized by the NBR_ADV message (i.e., SINRs of pilotsignals transferred from the neighbor BSs) according to parameterscontained in the SCANNING_IE message contained in the DL_MAP message atstep 1015. It should be noted that SINRs of pilot signals transferredfrom the neighbor BSs and the SINR of the pilot signal transferred fromthe BS 1050 to which the MSS 1000 currently belongs are continuouslyscanned, even though it is not illustrated in FIG. 10.

[0111] After scanning SINRs of pilot signals transferred from the activeBS (i.e., the BS 1050) and neighbor BSs, the MSS transmits theSCAN_REPORT message including the SINRs of the scanned BS 1050 andneighbor BSs to the BS 1050 at step 1017. The scan report operation forthe event “a” allows the MSS 1000 to firstly report pilot SINRs of theBS 1050 and neighbor BSs to the BS 1050, and then re-performs the scanreport operation only when the order of magnitudes of the pilot SINRs ofthe initially-reported BS 1050 and neighbor BSs is changed to anotherorder, such that the MSS 1000 initially performs the scan reportoperation only once.

[0112] Accordingly, the MSS 1000 transmits the SCAN_REPORT message tothe BS 1050, and scans pilot SIRs of the BS 1050 and neighbor BSsaccording to parameters contained in the SCANNING_IE message at step1019. If the event “a” occurs during the scanning time of the SINRs ofthe pilot signals transferred from the BS 1050 and neighbor BSs, i.e.,if there arises a variation in the magnitude order of pilot SINRs of theneighbor BSs even though the magnitudes of the pilot SINRs of the BS1050 are higher than the pilot SIlRs of the neighbor BSs at step 1021,the MSS 1000 transmits the SCAN_REPORT message including the SINRs ofthe scanned neighbor BSs to the BS 1050 at step 1023. The MSS 1000transmits the SCAN_REPORT message to the BS 1050, and scans pilot SINRsof the BS 1050 and neighbor BSs according to parameters contained in theSCANNING_IE message at step 1025. The MSS 1000 reports pilot SINRs ofthe BS 1050 and neighbor BSs to the BS 1050 only in the case ofgenerating the event “a”, such that it uses minimum resources for thescan report operation, resulting in increased overall efficiency ofsystem resources.

[0113]FIG. 11 is a flow chart illustrating a pilot SINR scan reportprocedure in accordance with a fifth preferred embodiment of the presentinvention. It is assumed that the scan report method is adapted to thescan report method based on the event “b” occurrence in FIG. 11.

[0114] Referring to FIG. 11, the BS 1150 transmits a DL_MAP messageincluding the SCAN_REPORT_IE message to the MSS 1100 at step 1111. TheSCAN_REPORT_IE message includes the same parameters as in Table 14. Thescan report method is based on the occurrence of the event “b”, suchthat the Event “b” mode value is determined to be a value of 1. TheDL_MAP message also includes the SCANNING_IE message for the MSS 1100'sscanning operation, and the SCANNING_IE message is shown above in Tables10 to 12.

[0115] The BS 1150 transmits the DL_MAP message including theSCAN_REPORT_IE and SCANNING_IE messages to the MSS 1100, and transmitsthe NBR_ADV message to the MSS 1100 at step 1113. In this case, theNBR_ADV message is the same as in Table 4 of the prior art, such thatits detailed description will herein be omitted.

[0116] The MSS 1100, having received the NBR_ADV message including theinformation associated with the neighbor BSs from the BS 1150, scansneighbor BSs recognized by the NBR_ADV message (i.e., SINRs of pilotsignals transferred from the neighbor BSs) according to parameterscontained in the SCANNING_IE message contained in the DL_MAP message atstep 1115. It should be noted that SINRs of pilot signals transferredfrom the neighbor BSs and the SINR of the pilot signal transferred fromthe BS 1150 to which the MSS 1100 currently belongs are continuouslyscanned, even though it is not illustrated in FIG. 11.

[0117] If the MSS 1100 decides to change its current active BS toanother BS while scanning SINRs of pilot signals of the neighbor BSs atstep 1117, i.e., if the MSS 1100 decides to change its current active BSto a new BS different from the BS 1150 at step 1117, the MSS 1100transmits the MSSHO_REQ message to the BS 1150 at step 1119. In thiscase, the MSSHO_REQ message must include IEs of the SCAN_REPORT messageas described above.

[0118] After transmitting the MSSHO_REQ message to the BS 1150, the MSS1100 re-scans pilot SINRs of neighbor BSs according to parameterscontained in the SCANNING_IE message at step 1121. The MSS 1100 reportspilot SINRs of the BS 1150 (i.e., an active BS) and neighbor BSs to theBS 1150 only in the case of generating the event “b”, such that itminimizes the amount of resources needed for the scan report operation,resulting in increased overall efficiency of system resources.

[0119] As is apparent from the above description, the present inventionprovides a method for measuring and reporting a channel quality (i.e., apilot SINR) in the IEEE 802.16e communication system used in a broadbandwireless access (BWA) communication system for use with an OFDM/OFDMAscheme. The present invention enables an MSS to scan pilot SINRs ofneighbor BSs even though there is no request from the MSS. Therefore, ifthe active BS for transmitting a desired service to the MSS is changedto another BS due to the MSS's mobility, the present invention performsa handover function associated with the changed active BS according topilot SIMR scanning result data of the MSS.

[0120] Although preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions, and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A method for measuring channel qualities of an active BS (Base Station) and a plurality neighbor BSs when an MSS (Mobile Subscriber Station) is located in an area covered by the active BS and the plurality of neighbor BSs in a communication system including the MSS, the active BS for providing the MSS with a desired service, and the plurality of neighbor BSs being adjacent to the active BS, comprising the steps of: a) transmitting channel quality measurement information needed for the MSS to measure channel qualities of the active BS and the neighbor BSs, from the active BS to the MSS; b) transmitting neighbor BS-associated information associated with the neighbor BSs, from the active BS to the MSS; and c) measuring at least one channel quality according to the channel quality measurement information of the active BS and the neighbor BSs associated with the neighbor BS-associated information.
 2. The method as set forth in claim 1, wherein the channel quality measurement information includes a measurement start time at which a channel quality measurement operation begins, and a measurement duration for executing the channel quality measurement operation.
 3. The method as set forth in claim 1, wherein the neighbor BS-associated information includes BS-IDs (Base Station Identifiers) for each of the neighbor BSs and physical channel frequencies for use in each of the neighbor BSs.
 4. The method as set forth in claim 1, wherein the step (c) for measuring the at least one channel quality of the active BS and the neighbor BSs comprises the steps of: c1) receiving reference channel signals received from the active BS and the neighbor BSs; and c2) measuring SINRs (Signal to Interference and Noise Ratios) of the reference channel signals of the neighbor BSs.
 5. The method as set forth in claim 1, further comprising the steps of: d) if the MSS decides to change the channel quality measurement information to other information, transmitting channel quality measurement information to be changed, and a change request of the channel quality measurement information to the active BS; and e) after receiving the channel quality measurement information change request, transmitting the changed channel quality measurement information, from the active BS to the MSS.
 6. The method as set forth in claim 5, wherein the channel quality measurement information includes a measurement start time at which a channel quality measurement operation begins, and a measurement duration for executing the channel quality measurement operation.
 7. The method as set forth in claim 6, wherein the MSS generates a change request signal of the measurement period contained in the channel quality measurement information.
 8. A method for reporting channel qualities of an active BS (Base Station) and a plurality of neighbor BSs measured by an MSS (Mobile Subscriber Station) to the active BS when the MSS is located in an area covered by the active BS and the neighbor BSs in a communication system including the MSS, the active BS for providing the MSS with a desired service, and the plurality of neighbor BSs being adjacent to the active BS, comprising the steps of: a) transmitting channel quality measurement information needed for the MSS to measure channel qualities of the active BS and the neighbor BSs, and other channel quality report information needed to report the channel qualities of the measured active BS and the measured neighbor BSs, from the active BS to the MSS; b) measuring, by the MSS, at least one channel quality according to the channel quality measurement information of the active BS and the neighbor BSs associated with neighbor BS-associated information; and c) transmitting the at least one channel qualities of the active BS and the neighbor BSs, from the MSS to the active BS, according to the other channel quality report information.
 9. The method as set forth in claim 8, wherein the other channel quality report information identifies a specific time at which the at least one channel quality is reported.
 10. The method as set forth in claim 9, wherein the channel quality report time is a predetermined setup period.
 11. The method as set forth in claim 10, wherein the MSS transmits the at least one channel qualities of the active BS and the neighbor BSs to the active BS at intervals of the predetermined setup period.
 12. The method as set forth in claim 9, wherein the step (b) for measuring the at least one channel qualities of the active BS and the neighbor BSs comprises the steps of: b1) receiving reference channel signals received from the active BS and the neighbor BSs; and b2) measuring SINRs (Signal to Interference and Noise Ratios) of the reference channel signals from the neighbor BSs.
 13. The method as set forth in claim 12, wherein the channel quality report time is a specific time during which a SINR of a reference channel signal received from the active BS is determined to be lower than either one of the SINRs of the reference channel signals received from the neighbor BSs, such that a determined state is maintained during a predetermined time.
 14. The method as set forth in claim 13, wherein the step (c) for transmitting the at least one channel qualities of the active BS and the neighbor BSs to the active BS according to the channel quality report information comprises the step of: c1) transmitting a handover request signal to a neighbor BS which has a reference channel's SINR higher than that of the active BS during the predetermined time.
 15. The method as set forth in claim 8, wherein the channel quality measurement information includes a measurement start time at which a channel quality measurement operation begins, and a measurement duration for executing the channel quality measurement operation.
 16. The method as set forth in claim 8, wherein the neighbor BS-associated information includes BS-IDs (Base Station Identifiers) for each of the neighbor BSs and physical channel frequencies for use in each of the neighbor BSs.
 17. A method for reporting channel qualities of an active BS (Base Station) and a plurality of neighbor BSs measured by an MSS (Mobile Subscriber Station) to the active BS when the MSS is located in an area covered by the active BS and the neighbor BSs in a communication system including the MSS, the active BS for providing the MSS with a desired service, and the plurality of neighbor BSs being adjacent to the active BS, comprising the steps of: a) transmitting channel quality measurement information needed for the MSS to measure channel qualities of the active BS and the neighbor BSs, and other channel quality report information needed to report the channel qualities of the measured active BS and the measured neighbor BSs, from the active BS to the MSS; b) measuring, by the MSS, at least one channel quality from the channel quality measurement information in association with the active BS and the neighbor BSs, associated with neighbor BS-associated information; c) transmitting the at least one channel qualities of the active BS and the neighbor BSs, from the MSS to the active BS; d) measuring, by the MSS, channel qualities of the active BS and the neighbor BSs according to the channel quality measurement information; and e) transmitting the channel qualities of the measured active BS and the neighbor BSs, in response to the other channel quality report information, from the MSS to the active BS.
 18. The method as set forth in claim 17, wherein the other channel quality report information identifies a specific time at which the channel quality is reported.
 19. The method as set forth in claim 18, wherein the step (b) for measuring the at least one channel qualities of the active BS and the neighbor BSs comprises the steps of: b1) receiving reference channel signals received from the active BS and the neighbor BSs; and b2) measuring SINRs (Signal to Interference and Noise Ratios) of the reference channel signals of the neighbor BSs.
 20. The method as set forth in claim 19, wherein the other channel quality report time identifies a specific time at which a magnitude order of SINRs of individual reference channel signals measured at the step (d) is different from other magnitude order of SINRs of reference channel signals of the neighbor BSs measured at the step (b).
 21. The method as set forth in claim 17, wherein the channel quality measurement information includes a measurement start time at which a channel quality measurement operation begins, and a measurement duration for executing the channel quality measurement operation.
 22. The method as set forth in claim 17, wherein the neighbor BS-associated information includes BS-IDs (Base Station Identifiers) for each of the neighbor BSs and physical channel frequencies for use in each of the neighbor BSs.
 23. A method for reporting channel qualities of an active BS (Base Station) and a plurality of neighbor BSs measured by an MSS (Mobile Subscriber Station) to the active BS when the MSS is located in an area covered by the active BS and the neighbor BSs in a communication system including the MSS, the active BS for providing the MSS with a desired service, and the plurality of neighbor BSs being adjacent to the active BS, comprising the steps of: a) receiving, from the active BS, channel quality report information indicative of channel periods of the channel qualities from the active BS, and receiving channel quality measurement information associated with individual channel qualities of the neighbor BSs and the active BS; b) measuring SINRs (Signal to Interference and Noise Ratios) of the neighbor BSs and the active BS according to the channel quality measurement information; and c) reporting the measured SINRs of the neighbor BSs and the active BS to the active BS according to a channel quality report period.
 24. The method as set forth in claim 23, wherein the channel quality report information identifies a specific time at which the measured SINRs are reported to the active BS.
 25. The method as set forth in claim 23, wherein the channel quality measurement information includes a measurement start time at which an operation for measuring SINRs of the neighbor BSs and the active BS begins, and a measurement duration during which the SINRs are measured. 